The study of bio-feedback is already an established research discipline. Bio-feedback systems exist, which are comprised of one or more sensors, for example sensors for galvanic skin response, local skin temperature, heart rate and heart rate variability, respiration, electromyography, electroencephalography etc. The aim of these systems is to extract certain physiological parameters out of the raw sensor signals that can, in this case, be interpreted in terms of emotional experience of the subject. The ongoing emotional experience can then be fed back to the user, preferably in real time, such that the user gets information about their state and can try to learn to control their bodily reactions and consequently also their emotions. Recently, the use of bio-feedback in lifestyle applications has become popular, for example, the introduction of massage devices with sensors, such as Sanyo massage-chair technology (see for United States of America Patent Application Publication US 2005/0137503).
Similar ideas are shown in U.S. Pat. No. 6,067,468, which discloses apparatus for monitoring a person's psycho-physiological condition. In this Patent the running of a program, designed to train the user to control one or more aspects of his or her psycho-physiological state, is controlled by signals representative of a psycho-physiological parameter of the user, for example, galvanic skin resistance. This may be detected by a sensor unit with two contacts on adjacent fingers of a user. The sensor unit is separate from a receiver unit which is connected to a computer running the program. It is the object of all of the known systems to provide accurate feedback to the subject about their current performance. Indeed an many applications, accuracy of the feedback is of paramount importance.